Color (or spectral) X-ray imaging has been identified as most promising route for future development of CT (Computer Tomography) by all vendors of medical CT scanners. However, CT vendors obviously follow different approaches to enter the spectral domain. This is mainly given due to the fact that hardware realization of a spectral CT scanner is a non-trivial task.
In a novel ‘inverse’ geometry CT (IGCT) system design, as described, for instance, in DeMan, B. et al., “Inverse geometry CT: The next-generation CT architecture?”, IEEE Nuclear Science Symposium Conference Record, 2007, M07-2, p. 2715-2716, a large distributed X-ray source with an array of discrete electron emitters and focal spots, and a high frame-rate flat-panel X-ray detector is used. With the advent of carbon-nanotubes (CNTs), as described, for instance, in Liu, Z. et al., “Carbon nanotube based microfocus field emission x-ray source for microcomputed tomography”, Applied Physics Letters 89, 103111 (2006), as cold ‘electron-guns’ fast switchable X-ray generators can be built. Such CNT-based X-ray sources can be arranged in an array-like manner in such an inverse CT system, where they are switched on and off in time according to a predetermined modulation pattern.
Known spectral CT systems have to overcome the following technical hurdles or have the following drawbacks:
Dual-source CT systems with dissimilar kVp (peak kilovoltage) settings: only two material components can be unambiguously separated; high hardware costs, since two sources and two detectors have to be mounted.
Dual-layer detector: only two material components can be unambiguously separated; complex production process of the detector.
Fast dual kVp switching: only two material components can be unambiguously separated; low spectral separation, since strong kV transients are difficult to realize.
Photon-counting spectral CT: detection requires high hardware effort.